The goal of the proposed research is to understand the processes that control differentiation of erythroid cells. The method of approach will be to analyze various properties of a permanent Friend leukemia virus transformed erythroleukemia cell line which can be induced to undergo a characteristic erythroid differentiation in cell culture. By comparing the control differentiation of these malignant cells with control of normal erythropoiesis we hope to elucidate how transformation with leukemic viruses alters these processes. We will study what controls are exerted during differentiation on the transcription and utilization of globin messenger RNA. Studies with whole cells will be complemented by in vitro experiments designed to study the transcription, processing and transport of globin mRNA in a cell-free system. UV transcription mapping will be used to study the size of the transcription unit of mouse and human globin genes. Cell hybrids expressing human globin genes will be used to study transcription and control of differential gene expression of the human gamma-delta-beta-gene locus. Another major area of investigation involves the use of cellular genetics for analyzing control of globin gene expression and the erythroid differentiation pathway. DNA mediated transformation of cells with cloned globin genes will be used to develop a system for studying potential cis-acting regulatory gene sequences. Studies of cell hybrids will lead to a better understanding of an X-linked, trans-acting locus controlling hemoglobin production. Cell hybrids, mutants and different culture conditions will be used to study the degree of coordinate control of several erythroid traits and to assess the cause-effect relationships in the differentiation pathway. With certain mutants we hope to better understand control of globin gene expression at the molecular level. These studies are relevant to an understanding of altered states of erythropoiesis, including the thalassemias and sideroblastic anemias.